1. they can't get out of the way; one can be stuck behind cars turning left (or broken down) for a long time.

2. they are heavy. They can shake the neighbourhood around them.

3. They are really noisy screeching around curves.

Skyscraper City

4. Track installation is incredibly disruptive and slow and really hard on the local businesses.

5. They can't pass; if one has a problem the entire system gets backed up.

I am not saying this to complain; I love our streetcars in Toronto and look forward to the new, fast, dedicated right of way that they are building on our local line. But they are not perfect. Ryan Avent notes some other issues:

Streetcars have a high upfront capital cost, which means they’re best suited to places with high ridership and lots of development potential. A lot of lower density neighborhoods will never satisfy those conditions, but would benefit from a reliable connection with the greater transit network, via bus. There’s a place for everything. The point is that transit offers a range of solutions to a range of traffic levels, densities, and community needs. Emphasizing the differences between streetcars and buses, rather than the everywhere-and-always superiority of the former, is key to building the rationale for a sensible transit network.